Rotary mechanical end face seals find wide application in pumps for pumping a liquid process fluid. As disclosed in U.S. Pat. No. 4,407,512, owned by John Crane Inc., Morton Grove, Ill., hydro-pad relieved areas, or depressions, on one of the relatively rotating seal faces is a configuration to enhance flow of process fluid between the relatively rotating sealing faces to provide a liquid film for lubrication. Typically, hydro-pad reliefs or depressions take the form of arcuate (scalloped) areas positioned at periodic intervals open at the peripheral edge of a seal face exposed to operating pressure of the process fluid. Typically such relieved areas have been formed to a depth of approximately 1.0 mm from the sealing face of the annular seal ring.
One common usage of rotary mechanical end face seals is found in power plant boiler feed water pumps. This application presents generally severe operating conditions, usually process fluid operating temperatures of 390° F. (200° Centigrade) at a pressure of 30 bar (450 psi).
Water at these pressures and temperatures is not a good lubricant. Because of the pressure drop across the seal face, the process fluid flashes to steam. It is common practice in such applications to provide separate cooling water flush for the seal to maintain its functionality, maintain reasonable durability and prevent excess leakage. Such auxiliary equipment and processing adds to both installation and incremental operating expense.
The arrangement disclosed here provides a seal for a boiler feed pump that does not require external cooling. It is configured to operate without any separate cooling water delivery system. It is an uncooled seal.